Mitosis division is the process in which two daughter cells each having the same number and kind of chromosomes as the parent nucleus are formed.
Karyokinesis is division of the nucleus. It consists of following four phases.
- First visible stage in karyokinesis.
- Chromosomes appear as long coiled threads called chromatids.
- Chromatins becomes shorter, thicker and visible due to the condensation of DNA.
- The chromatins are now called chromosomes.
- Stainability of nucleus increase.
- Each chromosome starts to splits longitudinally into two sister chromatids. These sister chromatids are attached with each other at centromere.
- The nuclear membrane and nucleolus starts to disappear and by the end it will completely disappeared.
- Nuclear membrane and nucleolus completely disappears and simultaneously appearance of spindle fibers.
- Spindle fibers attached to the centromere of chromosome and they are arranged on the equatorial plane.
- The process of gathering of chromosomes in equator is called congression and plate formed is called metaphasic plate.
- The centromere of each chromosome splits into two sister chromatids and forms two daughter chromosomes.
- The daughter chromosomes are pulled towards the poles due to contraction of spindle fibers and stretching of inter zonal fibers.
- During polar movement, the chromosomes shows different shapes i.e. J, U, V, L or I shaped in appearance.
- At the end of anaphase, each pole will get one set of daughter chromosomes.
- It is shortest phase and is also known as migratory phase.
- The daughter chromosomes reach respective poles, uncoil and become thin, long and visible.
- Spindle fibers start disappearing and finally disappear.
- Nuclear membrane and the nucleolus reappear.
- Two nuclei are formed at the end of telophase. Both the nuclei have same number of chromosome as parent cell.
- It is the last visible stage of karyokinesis and is also known as reorganization phase.
- Cytokinesis is division of the cytoplasm.
- In plant cells, cytokinesis occurs by cell plate formation.
- During cytokinesis, many granular matrixes formed by Golgi body and endoplasmic reticulum accumulates in the equatorial region. These granular matrix form cell plate which divides the cell.
- By the end of telophase, cytokinesis is completed.
- In animal cells, cytokinesis occurs by cleavage or furrow formation.
SIGNIFICANCE OF MITOSIS:
- Mitosis produces 2 genetically identical cells, thus maintains genetic stability of organisms.
- DNA remains constant, so mitosis keeps the chromosomes number constant in a species.
- Mitosis causes maturation and multiplication of germ cells and makes them ready for meiosis.
- Mitosis helps in the development of multicellular organism.
- Mitosis helps to replacement of old, dead or damaged cells by new one.
- It helps in the recovery of wounds and injury of the body by formation of new cells.
- In unicellular organisms like Paramecium, Yeasts etc. mitosis is a means of asexual reproduction.